Invention relates to fabrication of highly effective films for field emitters of electrons which can be used to produce flat panel displays, electron microscopes, microwave electronics, light sources and for some other applications.
Cold emission film cathode is known which comprises a substrate coated with a diamond film [Application of Diamond Films and Related Materials: Third International Conference, 1995, NIST Special Publication 885, Edited by A. Feldman et al., p. 37, p.61]. By the present date all attempts to create a highly effective emitter of electrons on a basis of polycrystalline diamond film can""t be considered to be successful, in particular, because of a low density of emission sites.
The most relevant to the present invention is a cold emission film cathode comprising a substrate coated with a carbon film [ less than  less than Diamond based field emission flat panel displays greater than  greater than Solid State Techn., 1995, May, p.71]. The film deposited on the substrate is a film of amorphous carbon.
A method is known to produce a cold emission film cathode by a method of laser sputtering [ less than  less than Diamond based field emission flat panel displays greater than  greater than Solid State Tech., 1995, May, p. 71], which comprises the deposition on a cold substrate of carbon evaporated from a graphite target by a powerful laser radiation. Shortcoming inherent to this method is its complexity, high cost, limited scaling up capability , and also the low density of emission sites ( about 1000 per sq.cm in the electrical field of 20 V/micron) what is apparently insufficient for creation of a full color display with 256 grades of brightness.
A method is known to produce a cold emission film cathode by a method of plasma chemical vapor deposition comprising a DC glow discharge in an electrode gap between cathode and anode in a flow of hydrogen, heating a substrate up to the deposition temperature, injection of a carbon containing gas into flow and deposition of a film from a mixture of hydrogen and carbon containing gas, removing of excessive graphite phase by a discharge in hydrogen flow [A. T. Rakhimov, B. V. Seleznev, N. V. Suetin et al. Applications of Diamond Films and Related Materials: Third International Conf., Gaithersburg, Md., USA, 1995, NISTIR 5692, Supplement NIST Special Publication 885, p.lIs]. Thus the nano-diamond film cathodes are produced. But the diamond films produced by this method grow very slowly and often do not possess emissive properties sufficient for creation of a full color display.
A method is known to produce a diamond cathode [U.S. Pat. No. 4,816,286, 1989] comprising a microwave discharge with input power of 100-1000 W in a mixture of carbon dioxide and methane with the ratio of 0.8-1.2 at pressure of 20-100 Torr and deposition of the carbon phase on a substrate. But this method is very costly and films produced by this method possess rather non uniform emissive performances.
The technical goal of this invention is obtaining of a cold emission film cathode possessing high electron emissive performances which can be used as a field emitter of electrons for production of flat panel displays, electron microscopes, microwave electronics, light sources and for some other applications,
This task can be solved due to that the cold emission film cathode comprising a substrate coated with a carbon film deposited on it is made in the form of a structure of irregularly located carbon microxe2x80x94 and nano-ridges and/or microxe2x80x94 and nano-threads (tips) normally oriented to the substrate surface and having typical size of 0.01-1 micron and distribution density of 0.1-10 xcexcmxe2x88x922. The cathode can be produced by two methods.
Using the first method the cold emission film cathode is produced in a DC glow discharge in a mixture of hydrogen and carbon containing gas via deposition of a carbon film on a substrate placed on an anode. The DC glow discharge is ignited at a current density of 0.15-0.5 A/sq.cm, and deposition is carried out from a mixture of hydrogen and ethyl alcohol vapor or methane at total pressure of 50-300 Torr and substrate temperature of 600-900 C., and concentration of ethyl alcohol shall be 10-15% and concentration of methane shall be 15-30%.
Using the second method the cold emission film cathode is produced in a microwave discharge with input power of 5-50 W/cub.cm in a mixture of carbon dioxide and methane with the ratio of 0.8-1.2 at pressure of 20-100 Torr and deposition of the carbon phase on a substrate is carried out at the substrate temperature of 500-700 C.